Safety needle syringe braking system

ABSTRACT

A braking mechanism for a retractable safety syringe is disclosed herein. In a first embodiment, the braking mechanism is disposed about the distal end of a piston. The braking mechanism may comprise a friction material about a post attached to a piston. The friction material is displaced from a seat to a landing when the piston is traversed to a fully extended position to disengage the braking mechanism. In a second embodiment, the braking mechanism is disposed at a proximal end of a syringe body. The braking mechanism has a friction member which engages an outer surface of a rigid shaft of a plunger. The friction member is selectively pivotable to disengage the braking mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional PatentApplication No. 60/788,796, filed Apr. 3, 2006.

STATEMENT: FEDERALLY SPONSORED RESEARCH/DEVELOPEMENT

Not Applicable

BACKGROUND

The present invention relates to a retractable safety syringe, and moreparticularly, to a braking mechanism to resist a retraction force duringnormal operation of the retractable safety syringe until a piston headengages a needle holder and needle to then withdraw the needle holderand needle within the safety syringe body.

Retractable safety syringes are known in the art. For example, one typeof retractable safety syringe is disclosed in U.S. Pat. No. 6,413,236issued to Van Dyke, the entire contents of which are incorporated hereinby reference. In the '236 patent, a retractable safety syringe has apiston which engages a needle holder and needle and retracts the samevia a retraction force created by a variable vacuum compartment. In theretractable safety syringe disclosed in the '236 patent, the user mustcontinuously apply a thumb pressure on the thumb platform such that thepiston is not inadvertently traversed to a retracted position duringoperation of the safety syringe. For example, the piston may beinadvertently traversed to the retracted position while medication isbeing filled in a variable fluid chamber, residual air is being ejectedfrom the variable fluid chamber and medication is being injected intothe patient. As such, the user or medical professional is required toreceive additional training to operate the safety syringe properly andsafely. Unfortunately, the additional training may be costly. Also,since the operation of the safety syringe is not intuitive or foolproof, mistakes may be made during operation of the safety syringe.

Accordingly, there is a need in the art for an improved safety syringe.

BRIEF SUMMARY

The retractable safety syringe disclosed herein addresses the needsdiscussed above, below and those that are known in the art.

In a first embodiment of the retractable safety syringe, a brakingmechanism is disposed adjacent a distal end of the safety syringe. Inparticular, the braking mechanism may comprise a friction materialattached to a piston of the safety syringe. The friction materialfrictionally engages the inner surface of the syringe body to resisttraversal of the piston head toward a retracted position. The brakingmechanism may also comprise a punch attached to the distal end of thesyringe body. When the piston head is traversed between the retractedposition and an extended position, the friction material maintainsfrictional engagement with the inner surface of the syringe body. Whenthe piston head is traversed to the fully extended position, the punchdisengages the friction material from the inner surface of the syringebody.

The friction material may be attached to the piston head via two tines.The two tines may define a seat and a landing. When the frictionmaterial is disposed about the seat, the friction material frictionallyengages the inner surface of the syringe body producing a friction forcegreater than or equal to about a retraction force of a variable vacuumcompartment. When the friction material is disposed about the landing,the friction material creates a friction force against the inner surfaceof the syringe body which is less than the retraction force created bythe variable vacuum compartment.

The punch may have a fulcrum which intersects the interface between thefriction material and the two tines when the piston head is traversed tothe fully extended position. The punch may also have a frusto-conicalsurface which engages the distal ends of the two tines and is operativeto inwardly displace the two tines to release the friction material fromthe seat. As the piston head is traversed from the extended position tothe fully extended position, the frusto-conical surface displaces thetwo tines inwardly and the punch pushes the friction material off of theseat and onto the landing. The tines have pawl surfaces which springoutwardly and engage cam edges of the needle holder when the piston headis traversed to the fully extended position. At this point, theretraction force then withdraws the needle and needle holder into thesyringe body.

In a second embodiment of the retractable safety syringe, a secondembodiment of the braking mechanism is provided. The second embodimentof the braking mechanism may comprise a base member and a frictionmember which are pivotable with respect to each other about a joint. Thefriction member has an up position and a down position. In the upposition, an inner edge of a central aperture formed in the frictionmember frictionally engages a rigid shaft. Such frictional engagementproduces a friction force which is greater than or equal to about theretraction force of the variable vacuum compartment. As the piston headis traversed between the retracted position and the extended positionduring operation of the safety syringe, the friction force of thefriction member prevents traversal of the piston head toward theretracted position.

When the piston head is traversed to the fully extended position, abottom surface of a thumb platform pushes down on the top surface of thefriction member to traverse the friction member to the down position. Inthe down position, a pawl of the friction member engages a cam of thebase member. As such, the friction member is not permitted to pivot backto the up position. Also, at the down position, the inner edge of thecentral aperture of the friction member disengages the outer surface ofthe rigid shaft thereby reducing or eliminating the friction force. Thepiston head also engages the needle and needle holder via any means thatare known in the art or by means discussed in the first embodiment.Since the friction force of the friction member no longer acts on theouter surface of the rigid shaft, the retraction force of the variablevacuum compartment then withdraws the needle holder and needle into thebody of the safety syringe.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is an exploded front view of a safety syringe illustrating afirst embodiment of a braking mechanism;

FIG. 2 is an assembled front view of the safety syringe of FIG. 1;

FIG. 2 a is an enlarged front view of the safety syringe of FIG. 2 witha second seal unassembled from a piston and a friction materialunassembled from two tines;

FIG. 3 is a front view of the safety syringe with the friction materialengaged to a punch and the piston in an extended position;

FIG. 4 is a front view of the safety syringe with a fulcrum of a punchintersecting an interface of the friction material and two tines and thefriction material being displaced from a seat to a landing;

FIG. 5 is a front view of the safety syringe with the friction materialdisposed about the landing and the piston in a fully extended position;

FIG. 6 is an enlarged assembled view of FIG. 2 a;

FIG. 7A is a top view of the two tines and a first embodiment of thefriction material;

FIG. 7B is a top view of the two tines and a second embodiment of thefriction material;

FIG. 7C is a top view of the two tines and third embodiment of thefriction material;

FIG. 8 is a front view of a second embodiment of the braking mechanismdisposed about a proximal end of the syringe body;

FIG. 9A is a top view of the braking mechanism illustrating an edge ofan aperture formed in a friction member in friction engagement with arigid shaft of the safety syringe;

FIG. 9B is a top view of a base member of the braking mechanism with anaperture sized and configured to slidably receive the rigid shaft;

FIG. 10 is a front view of the braking mechanism with the frictionmember disengaged from the rigid shaft;

FIG. 11 is a top view of the braking mechanism illustrating that theedge of the aperture formed in the friction member is disengaged fromthe rigid shaft when the friction member is locked on the base; and

FIG. 12 is an assembled front view of the safety syringe of FIG. 1wherein a retraction force urging a piston toward a retracted positionis created by a tension spring.

DETAILED DESCRIPTION

Referring now to the drawings which are for the purpose of illustratingpreferred embodiments of a retractable safety syringe 10 and not for thepurpose of limiting the same, FIGS. 1-7C illustrate a first embodimentof the retractable safety syringe 10. Also, FIGS. 8-11 illustrate asecond embodiment of the retractable safety syringe 10.

FIG. 1 is an exploded view of the first embodiment of the retractablesafety syringe 10. FIG. 2 is an assembled view of the first embodimentof the retractable safety syringe 10 shown in FIG. 1. A plunger 12 isdisposed at a proximal side of a syringe body 14. Also, a needle holder16 and needle 18 are disposed at a distal side of the syringe body 14.An attachment base 20 may be attached to a proximal end of the syringebody 14. Furthermore, a first seal 22 may be disposed about an innerperiphery of the attachment base 20. Finger platforms 24 may also beformed at the proximal end of the body 14 which may be utilized tooperate the syringe 10.

The plunger 12 may have a piston 26 (see FIG. 1) disposed within thesyringe body 14, as shown in FIG. 2. The piston 26 may have a pistonhead 28 and a second seal 30 which is in sealing contact with the pistonhead 28 and an inner surface 32 of the syringe body 14. The second seal30 forms an air tight and a fluid tight seal between the piston head 28and inner surface 32 of the syringe body 14. The plunger 12 may alsohave a rigid shaft 34 connected to the piston head 28 and extendedthrough the proximal end of the syringe body 14 (see FIG. 2). The rigidshaft 34 may be in sealing contact with the first seal 22. The firstseal 22 also forms an air tight and a fluid tight seal between theattachment base 20 and the rigid shaft 34. A thumb platform 36 may alsobe attached to the rigid shaft 34 at a proximal end thereof.

The thumb platform 36 and the finger platforms 24 work in conjunctionwith each other such that the user may depress the thumb platform 36toward the finger platform 24 by pressing the thumb platform 36 withhis/her thumb. This traverses the piston head 28 from a retractedposition (see FIGS. 2 and 6) to an extended position or first extendedposition (see FIG. 3) or a fully extended position or second extendedposition (see FIG. 5). The piston head 28 may also be traversed from theextended position or first extended position to the retracted positionby simultaneously pulling on the thumb platform 36 while pushing on thefinger platforms 24. In relation to the first embodiment of the safetysyringe, generally, the retracted position is when the piston 26 iscloser to the proximal end of the body 14 than the distal end of thebody. But, the retracted position may include situations when the piston26 does not contact the needle holder 16 and the piston 26 is closer tothe distal end of the body 14 than the proximal end of the body 14. Theextended position or first extended position is generally when thepiston 26 is closely adjacent to the needle holder 16 or in contact withthe needle holder 16 and the piston 26 is not engaged to the needleholder 16. The fully extended position or second extended position iswhen the piston 26 is in contact with the needle holder 16 and engagedto the needle holder 16.

The cavity between the first and second seals 22, 30 within the syringebody 14 defines a variable vacuum compartment 38. The variable vacuumcompartment 38 creates a retraction force when the piston head istraversed to the extended position or first extended position urging thepiston head 28 toward the retracted position. As the piston head 28 istraversed from the retracted position to the extended position (firstextended position) or fully extended position (second extendedposition), the retraction force created by the variable vacuumcompartment 38 increases.

The needle holder 16 and needle 18 are disposed or attached to thedistal end of the syringe body 14. Furthermore, the cavity between thepiston head 28 and the needle holder 16 within the syringe body 14defines a variable fluid chamber 40 in which fluidic medication may befilled and subsequently injected into a patient.

In operation, the retractable safety syringe 10 is provided to a user ormedical professional with the piston head 28 in the retracted position.To fill the variable fluid chamber 40 with medication, the piston head28 is traversed to the extended position or first extended position bydepressing the thumb platform 36 toward the finger platform 24. At theextended position or first extended position, the needle 18 is insertedinto a medication container containing fluidic medication. The user thentraverses the piston head 28 from the extended position or firstextended position to the retracted position thereby filling the variablefluid chamber 40 with medication. The user then inverts the syringe 10and slightly depresses the thumb platform 36 toward the finger platform24 to remove any residual air within the variable fluid chamber 40. Theuser then inserts the needle 18 into the patient's skin and depressesthe thumb platform 36 toward the finger platform 24 thereby injectingthe medication into the patient.

In the above description of the retractable safety syringe 10, as thepiston head 28 is traversed to the extended position or first extendedposition, the retraction force continuously urges the piston head 28toward the proximal end of the syringe body 14. But for a brakingmechanism, the user must overcome the retraction force by applyingcontinuous pressure on the thumb platform 36 greater than or equal tothe retraction force. Fortunately, in the first embodiment of theretractable safety syringe 10, a braking mechanism is incorporatedtherein to prevent the automatic and unintended retraction of the pistonhead 28 toward the proximal end of the syringe body 14. In particular,as shown in FIG. 2A, the braking mechanism may have a post 42 defining aseat 44 and a landing 46. A friction material 48 may be disposed aboutthe seat 44 or the landing 46 (see FIGS. 1-3 and 5). When the frictionmaterial 48 is disposed about the seat 44, the outer periphery of thefriction material 48 engages the inner surface 32 of the syringe body 14and applies a frictional force thereto which is greater than or aboutequal to the retraction force of the variable vacuum compartment 38.

The friction material 48 is also displaceable from the seat 44 to thelanding 46 (see FIG. 5). When the friction material 48 is disposed aboutthe landing 46, the outer periphery of the friction material 48 maycreate a friction force which is less than the retraction force of thevariable vacuum compartment 38. In the above described operation of theretractable safety syringe 10, the friction material is retained aboutthe seat 44 during the entire operation of the retractable safetysyringe 10 except when the piston head 28 is traversed to the fullyextended position or second extended position (see FIG. 5) at whichpoint, the friction material 48 is displaced from about the seat 44 toabout the landing 46.

When the friction material 48 is disposed about the seat 44, thefriction material 48 permits the user to traverse the piston 26 betweenthe retracted position and the extended position or first extendedposition without balancing a pressure applied to the thumb platform 36and the retraction force of the variable vacuum compartment 38. Forexample, the user does not have to balance such pressures when themedication is being filled within the variable fluid chamber 40 or airis being removed from the variable fluid chamber 40. The piston head 28is not permitted to traverse back toward the retracted position via theretraction force thereby the variable fluid chamber 40 is not filledwith excessive medication and air is not reintroduced into the variablefluid chamber 40.

To displace the friction material 48 from the seat 44 to about thelanding 46, the post 42 may be fabricated from two tines 50 having anupper portion (i.e., landing 46) and a lower portion (i.e., seat 44), asshown in FIG. 2A. The upper portion defines the landing 46 and the lowerportion defines the seat 44. The two tines 50 are bendable toward eachother by applying a compressive force at the distal ends of the twotines 50. When the compressive force is released, the two tines 50 aredisplaced outwardly. The upper portion or landing 46 may have an outerperiphery which may be sized to an inner periphery of the frictionmaterial 48 such that the frictional force of the friction material 48on the inner surface 32 of the syringe body 14 is less than theretraction force created by the variable vacuum compartment 38 when thefriction material 48 is disposed about the landing 46. The outerperiphery of the lower portion or seat 44 may be sized to the innerperiphery of the friction material 48 such that the frictional forcecreated by the friction material 48 on the inner surface of the syringebody 32 is greater than or about equal to the retraction force of thevariable vacuum compartment 38 when the friction material 48 is disposedabout the seat 44. To displace the friction material 48 from the seat 44toward the landing 46, a punch 52 (see FIGS. 2A and 6) may be formedabout a proximal end of the needle holder 16 which is operative to pushthe friction material 48 off of the seat 44 and onto the landing 46.Also, as discussed further below, the punch 52 is operative to inwardlydisplace the two tines 50 to reduce the outer periphery of the seat 44thereby permitting the friction material 48 to be displaced from theseat 44 to the landing 46.

The seat 44 of the two tines 50 may have an undercut groove which issized and configured to receive the friction material 48. The frictionmaterial 48 may have various configurations as shown in FIGS. 7A-7C. InFIG. 7A, the friction material 48 has a flat disk configuration; in FIG.7B, the friction material 48 has a flat cross configuration; and in FIG.7C, the friction material 48 has flat wheel rim configuration. When thefriction material 48 is disposed about the seat 44, the two tines 50apply an outward force upon the inner periphery of the friction material48. The under cut groove in combination with the outward force preventsthe friction material 48 from being displaced off of the seat 44 as thepiston head 28 is traversed between the retracted position and theextended position or first extended position.

The punch 52 may have a fulcrum 54 and a frusto-conical surface 56, asshown in FIGS. 2A and 6. When the piston 26 is traversed to the extendedposition or first extended position (see FIG. 3), the fulcrum 54 engagesthe interface 58 (see FIG. 6) between the friction material 48 and theunder cut groove formed in the seat 44. The frusto-conical surface 56also engages the distal ends of the two tines 50, as shown in FIG. 3.When the. piston 26 is further traversed to the fully extended positionor second extended position (see FIG. 5), the frusto-conical surface 56further inwardly displaces the two tines 50 (see FIG. 4) and the punch52 simultaneously pushes the friction material 48 off of the seat 44 andonto the landing 46. When the friction material 48 is fully displacedoff of the seat 44, the under cut groove of the seat 44 may engage a camedge 60 (see FIGS. 2A, 5 and 6) of the needle holder 16 to positivelylock the piston 26 to the needle holder 16 (see FIG. 5). Since the sumof the friction forces between the needle holder 16 and distal end ofthe body 14 as well as the friction material 48 and the inner surface 32of body 14 is less than the retraction force, the retraction force ofthe variable vacuum compartment 38 retracts the needle holder 16 intothe syringe body 14.

In operation, the retractable safety syringe 10 of the first embodimentpermits the piston 26 to be traversed between the extended position(first extended position) (see FIG. 3) and the retracted position. Atany of these positions, due to the braking mechanism, the pressureapplied to the thumb platform 36 may be removed without the retractionforce of the variable vacuum compartment 38 retracting the piston 26toward the retracted position. Advantageously, the braking mechanismpermits the user to release thumb pressure from the thumb platform 36during operation of the retractable safety syringe 10 without the pistonhead 28 being immediately and unintentionally displaced toward theproximal end of the syringe body 14.

When the medication within the variable fluid chamber 40 is beinginjected into a patient, the piston head 28 is traversed to the fullyextended position or second extended position (see FIG. 5). As thepiston head 28 is traversed from the extended position or first extendedposition (see FIG. 3) to the fully extended position or second extendedposition (see FIG. 5), the punch 52 pushes the friction material 48 offof the seat 44 and onto the landing 46. Also, the frusto-conical surface56 of the punch 52 inwardly displaces the tines 50 such that thefriction material 48 is released from the under cut groove of the seat44. When the piston 26 is traversed to the fully extended position orsecond extended position, the friction material 48 is displaced over thelanding 46 and the under cut groove of the seat 44 receives thefrusto-conical surface 56. Also, the under cut groove of the seat 44engages the cam edge 60 of the punch 52. At this point, the sum of thefrictional forces exerted on the inner surface of the syringe body 32 bythe frictional material 48 as well as the needle holder 16 and thedistal end of the body 14 is less than the retraction force created bythe variable vacuum compartment 38. The needle holder 16 and needle 18have a sliding friction fit with the syringe body 14. The retractionforce may now withdraw the needle 18 and needle holder 16 within thesyringe body 14.

Referring now to FIGS. 8-11, a second embodiment of the retractablesafety syringe 10 is shown for the purposes of illustration and notlimitation. In FIG. 8, a second embodiment of the braking mechanism isdisposed or attached to a proximal end of the syringe body 14. Thebraking mechanism has a base member 100 and a friction member 102 whichare pivotable with respect to each other about a joint 104. The basemember 100 may be wider than the outer diameter of the syringe body 14and may replace the finger platforms 24 discussed in the firstembodiment of the retractable safety syringe 10. The base member 100 mayhave a central aperture 106 (see FIG. 9B) through which the rigid shaft34 of the plunger 12 is disposed. As shown in FIG. 9B, the rigid shaft34 is freely slidable through the central aperture 106 of the basemember 100.

The friction member 102 may also have an aperture 108 having anelliptical shape which is sized and configured to engage the rigid shaft34 when the friction member 102 is in an up position (see FIGS. 8 and9A) and disengage the rigid shaft 34 when the friction member 102 is ina down position (see FIGS. 10 and 11). In the up position, a pawl 110 ofthe friction member 102 rides or interferes with a cam 112 formed on adistal end of the base member 100. Also, in the up position, an inneredge of the central aperture 108 formed in the friction member 102frictionally engages the outer surface 114 of the rigid shaft 34, asshown in FIG. 9A. Such friction engagement may be greater than or equalto about the retraction force created by the variable vacuum compartment38. Moreover, the frictional forces between the inner edge of centralaperture 108 formed in the friction member 102 and the outer surface 114of the rigid shaft 34 is less than the force required to displace thepawl 110 over the cam 112.

During the step of filling the variable fluid chamber 40 with medicationand removing air from the variable fluid chamber 40, the frictionalforce created between the friction member 102 and the rigid shaft 34 issufficient to hold the piston head 28 at any position between theretracted position and the extended position or first extended position.When the piston head 28 is traversed to the fully extended position orsecond extended position, a bottom surface of the thumb platform 36pushes against the top surface of the friction member 102 until the pawl110 is permitted to slide over the cam 112 and engage the cam 112 (seeFIG. 10). The pawl 110 having a U-shaped or J-shaped configuration locksthe cam 112 within a throat of the pawl 110, as shown in FIG. 10. At thedown position, as shown in FIG. 11, the inner edge of the centralaperture 108 formed in the friction member 102 disengages the outersurface 114 of the rigid shaft 34 thereby eliminating the frictionforce. When the piston head 28 is traversed to the fully extendedposition or second extended position, the piston head 28 may be engagedto the needle 18 and needle holder 16 via any method known in the art orvia the structure discussed in relation to the first embodiment. At thefully extended position or second extended position, the brakingmechanism is disengaged and the retraction force of the variable vacuumchamber 38 withdraws the piston 26, needle 18 and needle holder 16within the syringe body 14.

In relation to the second embodiment of the safety syringe, generally,the retracted position is when the piston 26 is closer to the proximalend of the body 14 compared to the distal end of the body 14. But, theretracted position may include situations when the piston 26 does notcontact the needle holder 16 and the piston 26 is closer to the distalend of the body 14 compared to the proximal end of the body 14.Additionally, at the retracted position, the thumb platform 36 does notcontact the friction member 102. The extended position or first extendedposition is when the piston 26 is closely adjacent to the needle holder16 or in contact with the needle holder 16 and the piston 26 is notengaged to the needle holder 16. Additionally, at the extended positionor first extended position, the thumb platform 36 may be closelyadjacent to the friction member 102 or in contact with the frictionmember 102. Nonetheless, the pawl 110 is not engaged to the cam 112. Thefully extended position or second extended position is when the piston26 is in contact with the needle holder 16 and engaged to the needleholder 16. Also, at the fully extended position the thumb platform 36may be in contact with the friction member 102.

In an aspect of the retractable safety syringes 10 of the first andsecond embodiments, the braking mechanisms may be employed inretractable safety syringes that are spring activated. For example, FIG.12 illustrates a retractable safety syringe 10 having a similarconfiguration to the first embodiment of the safety syringe 10. Inparticular, the variable vacuum compartment 38 may have at least one butpreferably two or more tension springs 130 attached to the proximal endof the body 14 and the piston 26. The tension springs 130 may be relaxedwhen the piston 26 is in the retracted position. When the piston 26 istraversed toward the extended position (first extended position) or thefully extended position (second extended position), the tension springs130 are tensioned so as to urge the piston 26 back toward the retractedposition. The tension springs 130 may create the retraction force whichurges the piston 26 back toward the retracted position. The retractionforce created by the tension springs 130 may be in addition to theretraction force created by the variable vacuum compartment 38.

Alternatively, the retraction force created by the tension springs 130may replace the retraction force of the variable vacuum compartment 38.To this end, an optional air vent 132 may be formed through the body 14of the syringe 10. The air vent 132 permits air to be introduced into orremoved from the cavity 134 previously identified as the variable vacuumcompartment 38. When the piston 26 is traversed toward the extendedposition (first extended position) or the fully extended position(second extended position), air is introduced into the cavity 134 viathe air vent 132. Hence, a vacuum is not formed in the cavity 134. Also,when the piston 26 is traversed toward the retracted position, air isremoved from the cavity 134 via the air vent 132. Hence, air is notcompressed within the cavity 134. When the air vent 132 is formedthrough the body 14 of the syringe 10, the retraction force is createdsolely by the tension springs 130. The safety syringe 10 shown in FIG.13 may be operated in a similar fashion as the first embodiment of thesafety syringe 10. Although the tension springs 130 were discussed inrelation to the first embodiment of the safety syringe 10, the tensionsprings 130 may also be employed in the second embodiment of the safetysyringe 10.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments.

1. A retractable safety syringe for preventing syringe reuse andaccidental needle pricking, the syringe comprising: a syringe bodydefining a distal end, proximal end and inner surface; a plunger havinga piston disposed within the syringe body, a rigid shaft extendingthrough the proximal end of the syringe body, and a thumb platformattached to the rigid shaft which is operative to traverse the pistonbetween a retracted position and a fully extended position, the pistonfurther having a braking mechanism comprising: a protuberance having aseat and a landing, an outer periphery of the seat being larger than theouter periphery of the landing; a friction material disposable about theseat or the landing, a maximum friction force between the frictionmaterial and the inner surface of the body being greater than or aboutequal to a retraction force of a retraction mechanism when the frictionmaterial is disposed about the seat, and the friction force between thefriction material and the inner surface of the body being less than theretraction force when the friction material is disposed about thelanding; and a punch attached to the distal end of the body andoperative to displace the friction material from the seat to the landingwhen the piston is traversed to the fully extended position.
 2. Thesyringe of claim 1, wherein the protuberance of the braking mechanismhas two tines, an outer periphery of the seat being larger than an innerperiphery of the friction material in a relaxed state, the tines beingbendable to fit the friction material about the seat.
 3. The syringe ofclaim 2, wherein the two tines further define the landing, the landingouter periphery being sufficiently smaller than the friction materialinner periphery such that the frictional force between the frictionmaterial and the inner surface of the syringe body is smaller than theretraction force when the friction material is disposed about thelanding.
 4. The syringe of claim 2, wherein distal ends of the tineshave an under cut groove to receive the inner periphery of the frictionmaterial.
 5. The syringe of claim 4, wherein the two tines are inwardlydisplaceable to release the friction material.
 6. The syringe of claim5, wherein the punch has a frusto-conical surface aligned to distal endsof the tines for receiving the distal ends of the tines and inwardlydisplacing the tines.
 7. The syringe of claim 6, wherein the punch has afulcrum aligned to an interface between the friction material and theseat for separating the friction material from the seat as the piston istraversed to the fully extended position.
 8. The syringe of claim 1wherein the retraction mechanism is a variable vacuum compartment. 9.The syringe of claim 1 wherein the retraction mechanism is a spring. 10.A retractable safety syringe for preventing syringe reuse and accidentalneedle pricking, the syringe comprising: a syringe body defining adistal end and a proximal end; a plunger having a piston disposed withinthe syringe body, a rigid shaft extending through the proximal end ofthe syringe body, and a thumb platform attached to the rigid shaft whichis operative to traverse the piston between a retracted position, afirst extended position, and a second extended, the plunger being biasedtoward the retracted position via a retraction mechanism; a brakingmechanism adjacent the proximal end of the syringe body, the brakingmechanism comprising: a friction member having a through hole, the rigidshaft slideably disposed through the through hole, the friction memberhaving an up position and a down position, an inner edge of the throughhole frictionally engages the rigid shaft to resist a retraction forceof the retraction mechanism that urges the plunger to the retractedposition when the friction member is in the up position and the inneredge of the through hole frictionally disengages the rigid shaft whenthe friction member is in the down position to permit the retractionforce to urge the plunger to the retracted position.
 11. The syringe ofclaim 10 wherein the friction member is rotateable between the upposition and the down position.
 12. The syringe of claim 10 wherein thefriction member further comprises a pawl for retaining the frictionmember in the down position when the pawl engages the proximal end ofthe syringe body and the inner edge of the through hole frictionallydisengages the rigid shaft.
 13. The syringe of claim 12 furthercomprising a base member, the friction member being pivotably attachedto the base member and the pawl being selectively attachable to the basemember.
 14. The syringe of claim 13 wherein the pawl has a J shape. 15.The syringe of claim 10 wherein a maximum frictional force between thefriction member and the rigid shaft is greater than or equal to aboutthe retraction force of the retraction mechanism.